The present invention relates to a gas supplying apparatus and a gas substitution method, more particularly to a gas supplying apparatus and a gas substitution method capable of carrying out gas substitution efficiently when plural kinds of high-purity gases are switched and supplied.
In the field of semiconductor industry, many gas-phase processes have been used in a device manufacturing process. It has been understood that if a very small amount of gas impurities exists in a high-purity bulk gas used in the gas-phase processes, the gas impurities have bad effects on the device performance. Therefore, a gas system for supplying high-purity gases is needed to avoid the situation where the gas system becomes a contaminating source of the impurities. Furthermore, the gas system must be capable of carrying out rapid substitution of a high-purity gas and of decreasing impurity concentration in a short time when a different high-purity gas commences to be supplied.
In the field of observing and analyzing impurity concentration in a high-purity gas, a high-sensitivity gas analyzing system using an analyzer such as an atmosphere pressure ionization mass spectrometer (AIPMS) if often employed. In the high-sensitivity gas analyzing system, there is a necessity that various kinds of gases be sequentially analyzed in a short time by using same analyzer. For this, since a prior gas having flowed becomes an impurity when gases are switched, rapid substitution in the gas system by a sample gas is required for a sampling system.
Generally, there exists, in a gas system, coupling parts or branching parts of pipes with a gas staying portion which has a bad effect on purge efficiency, an analyzer having an ion source with a complex structure and/or an analyzing column and detection unit, and a shutoff valve or a switching valve having many resin parts which hinder rapid purge by absorbing a gas, or the like. Therefore, when gas substitution in. a gas system is carried out, these parts determine rate control of the substitution of the entire gas system. As effecting purge methods in gas systems, a batch purge which fluctuates pressure from high pressure (xcx9c10 Mpa) to vacuum state (below 1 torr) to create a state of stopping the gas flow, or a flow purge with a high flow rate (litter/min) have been known.
However, these purge methods using high pressure or the load of a high volume of gasoline to flow rate when applied to the machinery or parts constitution a gas system become a cause of breakage or failure of parts and the like, such that there are many cases where the purge methods cannot be utilized. Therefore, since sometimes a measure to increase the flow rate to about several litters is necessarily taken, it takes a very long time in the gas substitution. In particular, when a high-purity gas whose impurity concentration is below parts per billion (hereinafter ppb) level is supplied, there is a need to carry out gas substitution sufficiently.
Therefore, the object of the present invention is to provide a gas supplying apparatus and a gas substitution method which does not damage the machinery and parts constituting the gas system, and which is capable of carrying out gas substitution in the gas system in a short time with good efficiency.
To achieve the above-mentioned object of the present invention, there is provided a gas supplying apparatus for switching and supplying plural kinds of gas, the apparatus comprising: a gas supplying passage; a gas exhaust passage connected to the gas supplying passage; a back pressure regulator provided in the gas supplying passage or the gas exhaust passage; a flow rate regulator provided in the gas supplying passage or the gas exhaust passage; and a control means for operating the back pressure regulator and the flow rate regulator with a predetermined sequence.
Furthermore, according to the present invention, there is provided a gas substitution method for substituting a gas after switching into a gas supplying passage by switching the kind of gases to be supplied, the method comprising the steps of: carrying out an operation for fluctuating pressure in the gas supplying passage within a range of pressure limitation of component parts thereof until a concentration of a gas before switching remaining in the gas supplying passage becomes ppb level when the gas after switching is made to flow in the gas supplying passage; setting the pressure to a predetermined pressure; and carrying out an operation for increasing flow rate of the gas after switching in the gas supplying passage under a flow rate limitation of the component parts thereof until the concentration of the gas before switching remaining in the gas supplying passage becomes sub-ppb level.
Furthermore, the method further comprises the steps of: providing a gas exhaust passage connected to the gas supplying passage; providing a back pressure regulator in the gas supplying passage or the gas exhaust passage; and providing a flow rate regulator in the gas supplying passage or the gas exhaust passage connected to the gas supplying passage; wherein the operation for fluctuating the pressure in the gas supplying passage is carried out by the back pressure regulator; and the operation for increasing the flow rate of a gas is carried out by the flow rate regulator.